Logic clip

ABSTRACT

A device which clips onto dual in-line integrated circuit (referred to herein as I.C.) package has a visual indicator for each pin or lead on the I.C. package to indicate the logic state on each pin or lead, and the device determines which leads are connected to the power supply and ground and uses the voltage across those leads to power itself.

United States Patent Gordon 1 51 June 13, 1972 [5 LOGIC CLIP 2,724,82111/1955 Schweitzer, Jr....................324/l27 X 3,076,901 2/1963Rubin et al [72] Imam" Cupmm 3,281,692 10/1966 Berose! ..324/133 x [73]Assignee: Hewlett-Packard Company, Palo Alto, 3,304,498 2/l967 Myers..324/ I 33 Calif.

[22] Filed: Much 5 1970 Primary Examiner-Rudolph V. Rolinec AssistantExaminer-Ernest F. Karlsen pp ,757 Attorney-A. C. Smith 52 us. c1...324/73 R, 324/51 ABSTRACT 1 1m. (:1. ..G0lr 15/12,G0lr 31 02 A devicewhich 2 ps onto dual m-llne integrated CIICLIII [58] 3 22; R 3?: 2 4 2(referred to herein as LC.) package has a visual indicator for I eachpin or lead on the LC. package to indicate the logic state I R I Citedon each pin or lead, and the device determines which leads are cconnected to the power supply and ground and uses the volt- UNITEDSTATES PATEMS age across those leads to power itself. 3,092,732 6/1963Milford ..324/103 P 7 Claims, 3 Drawing figures T 34 L? w P'ATENIEIIJIIII I3 1912 3.670.245 sum 1 or 3 REFERENCE VOLTAGE CIRCUIT GATE NETWORK L .J I

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mm as a INVENTOR. GARY B. GORDON LOGIC cur BACKGROUND OF THE INVENTIONWhen designing and servicing equipment with LC. logic modules, it isnecessary for the engineer or technician to know the logic states atvarious points in the equipment. Since these logic states arerepresented by discrete voltage levels which are present on the inputand output leads of the LC. s, the usual method of determining thestates has been to use an oscilloscope or a voltmeter to measure thevoltage on each lead. This method is slow and cumbersome, since only oneor two leads at a time can be tested, and the operator must divert hisattention away from the circuit under test to read the instrument. Also,since most logic circuits are binary in nature, the precise voltage isnot important to the operator, he desires to know only whether thevoltage is above or below some given threshold value. Recently a probehas been made available which has a light in it which is on when thevoltage is above the threshold and off when it is below. The probeovercomes some of the limitations of a voltmeter or oscilloscope, butone must still measure the voltage on the [.C. leads one by one, whichis a slow process when there are many leads. In addition, each of theaforementioned instruments requires power from some external source.

SUMMARY OF THE INVENTION The device of the present invention indicatesthe logic state on each lead or pin of an LC. simultaneously. The logicclip fastens to an LC. and has 16 visual indicators which are connectedto logic gates in the logic clip. A visual indicator is lit or on whenthe logic state on the lead or pin it represents is high or is an opencircuit and is off otherwise. The visual indicators are arranged in apattern which bears a one-to-one correspondence with the physicalarrangement of the leads on the LC. package. The present device does notrequire an external power supply or external power leads to connect to apower source and does not require a battery. Accordingly, the logic clipof the present invention incorporates a circuit which determines thepower and ground leads on the LC. under test and uses some of the poweron those leads to power itself.

DESCRIPTION OF THE DRAWINGS FIG. I shows a simplified schematic blockdiagram of the preferred embodiment.

FIG. 2 shows a schematic diagram of one of the logic state detectorsused in the preferred embodiment.

FIG. 3 shows the physical configuration of the preferred embodiment anda dual in-line integrated circuit package.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, there arel6 inputs I0, each of which is connected to a decision gate network 12and a threshold deteeter/amplifier 14. The detector/amplifier l4 drivesthe lightemitting diode (LED) 16. Elements 10, 12, 14 and 16 compriseone logic state detector 22. The logic clip is comprised of sixteenlogic state detectors 22 which share common positive supply voltage bus18 and ground bus 20. The decision gate network 12 decides whether theinput is connected to a ground, a supply or a logic lead on the LC. Ifinput 10 is connected to a supply lead, the decision gate networkconnects input 10 to supply bus 18, and all other logic state detectors22 receive supply voltage from the supply bus 18 through that input 10.If input 10 is connected to ground, the decision gate network connectsinput M to ground bus 20, and all other logic state detectors 22 areconnected to ground through ground bus to that input 10. If input 10 isconnected to a logic lead detector/amplifier 14 determines whether theinput voltage is above or below the threshold value 1.4 volt, and turnson LED 16 if the input is an open circuit or is above 1.4 volt. Eachlogic clip also includes a reference voltage circuit 23 which isconnected to supply bus 18 and ground bus 20. The reference voltagecircuit 23 supplies 2.1 volts to each detector/amplifier 14 throughreference bus 31.

FIG. 2 shows a schematic diam-am of one logic state detector 22. Diode36 connected between input 10 and supply bus 18 and diode 38 connectedbetween input 10 and ground bus 20 comprise the decision gate network12. Whichever input 10 is highest in voltage will forward bias diode 36and will therefore be connected to supply bus 18. Whichever input 10 islowest in voltage will forward bias diode 38 and will therefore beconnected to ground bus 20. Any input 10 with a logic level on it willbe a few tenths of a volt higher than ground and lower than the supplyvoltage due to the way l.C. logic circuits are designed, and thereforeboth diodes 3-6 and 38 will not be biased to conduction. Each logicstate detector 22 is connected to each other and the reference voltagecircuit at point 30 for supply voltage, at point 32 for the referencevoltage. and at point 34 for ground. Transistor 40 operates as thethreshold detector, with its emitter connected to input 10, its baseconnected to the supply bus 18 through a bias resistor 41, and itscollector connected to the base of transistor 44. Transistors 42 and 44form the LED 16 driver amplifier. LED 16 is connected between the supplybus 18 and the collector of transistor 42 so that LED 16 will turn onwhen transistor 42 is on or conducting. The base of transistor 42 isconnected to reference bus 31 and therefore is always at the referencevoltage 2.1 volts. The emitter or transistor 42 is connected to thecollector of transistor 44 through a bias resistor 43 and the emitter oftransistor 44 is connected to ground bus 20.

If input 10 is an open circuit, current will flow from the supply bus 18through the base-collector junction of transistor 40 and into the baseof transistor 44, which will allow transistor 44 to conduct. Whentransistor 44 conducts, transistor 42 conducts and LED 16 turns on. Thiseffect is consistent with the operation of many types of LC. circuits inwhich an open circuited lead is considered to be in the high logicstate. If the voltage on input 10 is higher than the threshold value 1.4volts current will still flow through the base-collector junction oftransistor 40 since its collector is at 1.4 volts. Since the activedevices in the preferred embodiment are all silicon semiconductordevices, there is a voltage drop across each diode junction of 0.7 voltswhen the diode is forward biased. Therefore, ground bus 20 will be 0.7volts higher than the ground lead on the LC. under test and the base oftransistor 44 will be at 1.4 volts with respect to ground. If thevoltage on input 10 is lower than l.4 volts, current will flow throughthe base-emitter junction of transistor 40 and turn it on, thus removingthe base bias current from transistor 44, which will turn it off andturn ofi' LED 16. This effect corresponds to a low logic state. Thereference voltage applied to the base of transistor 42 is to stabilizethe current through the LED 16.

FIG. 3 shows the physical configuration of the logic clip 11, withinputs l0 and light emitting diodes 16. The circuitry diagrammed in FIG.I is in the body of the device 54 along with light emitting diodes 16.Dual in-line integrated circuit 50 is shown having leads $2 emerging ina regularly spaced linear array from opposite sides 51. The logic clip11 fits over the integrated circuit 50 such that each input 10 contactsone lead 52. Squeezing sides 56 together near the top of the logic clip11 spreads apart the two rows of input leads 10 so the logic clip 10 canbe attached or removed from integrated circuit 50; and a springmechanism in logic clip 11 keeps the input leads 10 in contact with theintegrated circuit leads 52 when no pressure is applied to sides 56.

I claim:

1. A signalling apparatus comprising:

a plurality of inputs;

a reference signal bus;

gating means connected to each input and to the reference signal bus forconnecting an input having a potential extremum applied thereto to thereference signal bus to support current flow between the referencesignal bus and the input to which the potential extremum is applied, thegating means comprising a plurality of diodes, each diode having acathode electrode connected to a different input and an anode electrodeconnected to the reference signal bus; and

indicating means connected to each input and to the reference signal busfor indicating the signal level on each input with respect to the signallevel on the reference signal bus, the indicating means including aplurality of optical signalling devices; first circuit means forconnecting each optical signalling device to a differentinput; andsecond circuit means for connecting each optical signalling device tothe reference signal bus;

each optical signalling device giving an optical signal in response tothe signal level on the corresponding input exceeding a predeterminedthreshold value.

2. A signalling apparatus comprising:

a supply bus;

a plurality of inputs;

a reference signal bus;

gating means connected to each input and to the reference signal bus forconnecting an input having a lower potential extremurn applied theretoto the reference signal bus to support current flow between thereference signal bus and the input to which the lower potential extremumis applied, and connected to the supply bus for connecting an inputhaving a higher potential extremum applied thereto to the supply bus tosupport current flow between the supply bus and the input to which thehigher potential extremum is applied; and

indicating means connected to each input and to the reference signal busfor indicating the signal level on each input with respect to the signallevel on the reference signal bus, the supply bus being connected to theindicat ing means for supplying current to the indicating means.

3. A signalling apparatus as in claim 2 wherein:

the gating means comprises a first and second plurality of diodes, eachof the first plurality of diodes having a cathode electrode connected toa different input and an ing means comprises:

a threshold detector for each input. comprising an amplifier having aninput connected to one of the plurality of inputs. and having an outputwhich acts as a current source when its input is above a predeterminedpotential and acts as a current sink when its input is below apredetermined potential;

a driver amplifier for each input comprising an amplifier having aninput connected to the threshold detector output, and having an outputwhich acts as a current sink when current flows into its input and actsas an open circuit when no current flows into its input;

a light emitting device for each input, each device being connected tothe supply bus and the output of a driver amplifier for emitting lightwhen the driver amplifier output acts as a current sink and for emittingno light otherwise.

5. A signalling apparatus as in claim 4 wherein:

the inputs are physically disposed to electrically and mechanicallyconnect to the corresponding conductors of an integrated circuitpackage; and

the light emitting devices are physically arranged in a pattern whichbears a direct relationship to the physical arrangement of the leads ofthe integrated circuit.

6. A signalling apparatus as in claim 5 wherein the output of thethreshold detector acts as a current source when its input is opencircuited.

7. A signalling apparatus as in claim 6 wherein the light emittingdevices are light emitting diodes.

1. A signalling apparatus comprising: a plurality of inputs; a referencesignal bus; gating means connected to each input and to the referencesignal bus for connecting an input having a potential extremum appliedthereto to the reference signal bus to support current flow between thereference signal bus and the input to which the potential extremum isapplied, the gating means comprising a plurality of diodes, each diodehaving a cathode electrode connected to a different input and an anodeelectrode connected to the reference signal bus; and indicating meansconnected to each input and to the reference signal bus for indicatingthe signal level on each input with respect to the signal level on thereference signal bus, the indicating means including a plurality ofoptical signalling devices; first circuit means for connecting eachoptical signalling device to a different input; and second circuit meansfor connecting each optical signalling device to the reference signalbus; each optical signalling device giving an optical signal in responseto the signal level on the corresponding input exceeding a predeterminedthreshold value.
 2. A signalling apparatus comprising: a supply bus; aplurality of inputs; a reference signal bus; gating means connected toeach input and to the reference signal bus for connecting an inputhaving a lower potential extremum applied thereto to the referencesignal bus to support current flow between the reference signal bus andthe input to which the lower potential extremum is applied, andconnected to the supply bus for connecting an input having a higherpotential extremum applied thereto to the supply bus to support currentflow between the supply bus and the input to which the higher potentialextremum is applied; and indicating means connected to each input and tothe reference signal bus for indicating the signal level on each inputwith respect to the signal level on the reference signal bus, the supplybus being connected to the indicating means for supplying current to theindicating means.
 3. A signalling apparatus as in claim 2 wherein: thegating means comprises a first and second plurality of diodes, each ofthe first plurality of diodes having a cathode electrode connected to adifferent input and an anode electrode connected to the reference signalbus and each of the second plurality of diodes having an anode electrodeconnected to a different input and a cathode electrode connected to thesupply bus.
 4. A signalling apparatus as in claim 3 wherein theindicating means comprises: a threshold detector for each input,comprising an amplifier having an input connected to one of theplurality of inputs, and having an output which acts as a current sourcewhen its input is above a predetermined potential and acts as a currentsink when its input is below a predetermined potential; a driveramplifier for each input comprising an amplifier having an inputconnected to the threshold detector output, and having an output whichacts as a current sink when current flows into its input and acts as anopen circuit when no current flows into its input; a light emittingdevice for each inpuT, each device being connected to the supply bus andthe output of a driver amplifier for emitting light when the driveramplifier output acts as a current sink and for emitting no lightotherwise.
 5. A signalling apparatus as in claim 4 wherein: the inputsare physically disposed to electrically and mechanically connect to thecorresponding conductors of an integrated circuit package; and the lightemitting devices are physically arranged in a pattern which bears adirect relationship to the physical arrangement of the leads of theintegrated circuit.
 6. A signalling apparatus as in claim 5 wherein theoutput of the threshold detector acts as a current source when its inputis open circuited.
 7. A signalling apparatus as in claim 6 wherein thelight emitting devices are light emitting diodes.